1. Field of the Invention
The present invention relates to an optical projecting apparatus, and in particular to an optical projecting apparatus assembled by two digital micro-mirror devices (DMDs) and at least one solid state light sources.
2. Description of Related Art
Projector having light source consisted of laser and fluorescent material becomes popular. However, laser is expansive so that most of projectors having light source mentioned above adopt one chip digital light processing (DLP) technology to reduce cost.
Projector using one chip DLP technology includes only one digital micro-mirror device (DMD) to modulate image, so that a color wheel must be adopted to generate spectrums having various colors. For example, white spectrum generally composed of red spectrum, green spectrum, and blue spectrum. The spectrums are then serially transmitted to the DMD and modulated thereby, and then observers can sight colors corresponding to the spectrums created by persistence of vision.
The projector using one chip DLP technology mentioned above is compact and cheap because the projector includes only one DMD. However, the projector using one chip DLP technology can't meet requirement of luminance and color saturation. The projector using one chip DLP technology is limited to serial color modulation, so that luminance efficiency thereof is decreased. In order to compensate luminance efficiency, secondary color is applied to the projector mentioned above, however color saturation thereof is then decreased.
Besides, color breaking is brought by mechanical structure limitation of the color wheel. Namely, in some states, observer shall sight unpredictable scrambled color because serial color modulation can't meet condition of persistence of vision, so that the projector mentioned above can't satisfy with high-level application.
At present, projector using one chip DLP technology is replaced by that using three chips DLP technology to overcome color breaking and low luminance efficiency. Projector using three chips DLP technology includes three digital micro-mirror devices (DMDs) so that the single light source with white spectrum can be split into red spectrum, green spectrum, and blue spectrum by beam splitter(s). In the same time, the red spectrum, the green spectrum, and the blue spectrum are transmitted to the DMDs and processed thereby, so that problems of color breaking and low luminous efficiency can be overcome. However, the projector having three DMDs and peripheral optical component corresponding to the each DMD is bulky and its manufacturing cost is then increased.